How to calculate velocity?

[DrWhoF]

If you travel on a platform with speed of 250 000 km/s and you throw a ball with the same speed (250 000km/s) what will be the speed of the ball now?
C (light speed) is the highest speed known.

 

[padspcb]

Hi
Once ye ol"Newton said F=m*dQ/dt
So a Force can be expressed in a constant m currently known as mass times the variation of the Quantity of movement in time.
So the force neede to "throw" the object deppends in this formula.
Newton "never" said that dQ/dt == acceleration, this is a simplified aproach for low speed inertial systems.
The trouble is that in hi speed systems Q is also governed by 1/(c-v) where c=light speed and v is current speed. so to reach v=c F = X/0 or INFINITE.
You will never have the energy to throw the ball at such speed.
But these laws are only relevant to normal space, aka vacuum and no g field.
Imagine a graphics of s X t where s is space and t is time
If you draw a paralel line to t axis, you are stopped, no space change in time
If you draw a sloped line, the intersection is your s0 point and the declivity is your speed (ds/dt).
Imagine that the axis are such that in a declivity of 45 degrees (ds/dt = 1) you got the speed of light.
These lines are fixed, so you cannot have speeds more than 1c
But if you manage to create a "local" gravity field, this graphic is distorted, this already proven, and strange things happen.
Imagine a gravitational disturbance such that in your "local" disturbed timeframe you're at 100m/s, well below the 1c limit, so all laws are fine "locally" but you could be at 2c from an external observer, even if he only sees you at 1c.
Its more like, well, i must go to alpha-centauri, 4.5 light years, but my lame ship just goes at 10.000 km/h.
With a gravitational distortion, i could make alpha-centauri be at some 10.000 km away, like shrinking the universe, and my lame ship would take just 1 hour to get there.
Or better yet, get a platform that moves just 1 milimeter and with 1 step you travel across the world.
Trouble is that space is not 3D, but 6D, and time is a contant
Well, we have a long way to go, still in fire age....
When my kids were born there were no fax.... Does any one still uses fax????

Pads

 

[IanP]

Assuming, that this is just an accademic question, here is the answer:
If two velocities are added, according to Mr. Newton V=V1+V2, but according to Mr. Einstein V=(V1+V2)/(1+V1V2/C²).
In other words if one velocity were equal to the speed of light (in vacuum) adding another velocity to it would leave the total velocity at the light speed.
So, in your case, V1=250 000, V2=250 000, then V≈293 500 km/s (still below the speed of light.. ).
Regards,
IanP

 

[cedance]

hi,

for these sort of questions, i suggest u ask here... they can give u more than what u require....

/http://www.physlink.com

i have seen a similar question and an absolutely astounding reply there.. "what is the velocity with which a person should travel in the car so that the red light appears green".... hope this helps.

/cedance.